Personally, I have Heinie Straight Eight sights (with Trijicon Tritium inserts) on my G27 and you just can't go wrong with these. I've clover-leafed my first two shots of the day at the range less than an inch from the center X of a "reverse B-27" target.... at 25 yards (yeah... 75 feet).
You can check out the full story (with lots o' pics) from time of purchase onward here
: (New addition to my collection)